Since potatoes were brought to Europe from South America over 500 years ago it has become a common food to the extent that the United Nations declared 2008 the "Year of The Potato" because of its worldwide importance as a nutritious food. Most people can eat potatoes without harm, but it is not widely known that the potato is a member of the Nightshade group of plants, which includes deadly nightshade, tobacco, peppers, tomatoes, aubergines, and chillies.

Seven years ago Foods Matter published my description of the remarkable effects of potato on thirty-nine patients who were either allergic or intolerant of potato. This publication resulted in a steady stream of emails from all over the world describing a wide variety of illnesses caused by potato, and difficulties in convincing their doctors that potatoes could cause illness. My first publication describing allergy and intolerance to potato was published in a specialist journal nearly thirty years ago but aroused no interest whatever, in contrast to the response to publication on the internet in Foods Matter in 2004.

Since then I have continued to see occasional patients where potato caused a very wide variety of problems affecting different body systems. Obvious allergic reactions are uncommon, but delayed reactions characteristic of food intolerance are more frequent. Several sufferers had made the diagnosis themselves as a result of reading the section on potato in my website www.allergiesexplained.com. Reliable blood tests for intolerance to foods have not been invented, so do not waste money on the tests advertised or available in the health food shops. Blood tests for IgE mediated allergies and coeliac disease are available through the NHS.

Potato intolerance symptoms

Bloating, wind, colic, and diarrhoea, often labelled as "IBS" (Irritable Bowel Syndrome) are common manifestations of the effects on the gut which would be expected if a common food was irritating the bowels. Two cases had been diagnosed as Crohn's disease, but avoidance of potato was curative. When potato is digested traces of potato enter the bloodstream, so that any part of the body sensitive to potato will react, producing symptoms localisd to that part of the body. For example if the skin is sensitised eczema will appear, if the joints are sensitised they will become inflamed, or the nervous system will react with emotional or behavioural effects. This is why sufferers referred to a specialist clinic for the organ or system affected may find that the consultant does not know that food intolerance can cause problems in his speciality.

Quite a large number of responses were received from people who had found that peeling, scraping, or even touching potatoes causes itchy hands and skin reactions, usually solved by persuading a partner to do the potatoes, or using gloves. Scraping potatoes produces a very fine spray of juice which can cause itching of nose or eyes, and sometimes asthma. These people are probably allergic to potato and the allergy might become more extensive, so avoidance is sensible. Several had found that new potatoes produced much worse effects than old ones, explained by the fact that the solanine alkaloids are concentrated under the skin, and especially in the sprouts. (Another possibility in such a case is Oral Allergy Syndrome - Ed.)

There were many reports of all manner of effects on the nervous system, especially depression, anxiety, migraine or feeling confused and lethargic. Some children had gross misbehaviour, dyslexia, and learning difficulties which disappeared when potato was avoided, only to recur if a few crisps were given as a treat. In such cases there is nothing to lose by avoiding potatoes, tomatoes, aubergines, peppers and chillies for a trial period.

One respondent described how a breast fed baby aged two months screamed continuously until it was realised that mother was eating lots of new potatoes in their skins from the garden. When she stopped eating them he behaved normally, so he was not given potato until he was aged three, when he was given a few potato crisps. The result was that within minutes "he was transformed into a hyperactive little horror, climbing all over the furniture and misbehaving" His father adores potatoes and thinks he is being deprived, but every time he gives him crisps as a treat the result is awkwardness, misbehaviour, and refusal to go to bed. Several close relatives have food problems, including a cousin who gets eczema if she eats red tomatoes, not yellow ones, and has a craving for tomato sauce which results in eczema within two hours. A craving for a specific food can point to the food which is causing the problem!

Family sensitivity

The most striking recent case was a man aged 54 who had had asthma since childhood. He had discovered my website, which describes in detail the many problems which can be caused by potato, and decided to consult me. He was aware that a trace of milk or butter would cause severe asthma in half an hour, followed six hours later by bloating, colic, nausea, and finally terminated by diarrhoea. Even with strict avoidance of milk products he had severe chronic asthma and rhinitis which was very difficult to control, plus severe depression and shakiness. Inhalers containing steroid drugs in lactose powder, which may contain a trace of milk protein, caused asthma and he suspected that other foods might be involved .

The first important clue was in his family history. His eighty years old father had had lifelong "IBS", had had asthma and eczema when younger, he could not eat tomatoes because his mouth reacted to them, and he could not tolerate being in the same room as peppers, both members of the nightshade family. A grandson aged 23 has chronic asthma and had noted that spicy food caused colic and diarrhoea, probably due to chillies.

When he consulted me I found that a battery of forty skin and blood tests were all negative, but the sputum contained many eosinophil cells characteristic of allergic asthma. I suggested that he should avoid potato and all nightshade plants and exist on a diet of nothing but rice for a week. The result was that within only 24 hours his depression and shakiness vanished, along with the asthma, severe rhinitis, and all his gut symptoms. He was then instructed to live on a diet including only the few foods that rarely cause allergy or intolerance, and he remained well on this regime, and feels he has been given a new lease of life.

His peak flow readings increased progressively from around 220 to 350, and after some weeks to over 400, and he has remained well since. It would appear that he was already aware of some of his food intolerances, but had never considered the humble potato as the most important cause. When his condition had stabilised he was instructed to carry out test feeds with various foods to find out which caused reactions and must be avoided. An added bonus has been that when his father and the grandson were persuaded to avoid potato and all nightshade plants, father's life-long problems disappeared, and grandson's asthma also improved considerably. There were several other accounts of families where several members were affected in different ways which disappeared when nightshades were avoided, so there can be a genetic tendency to react against the nightshades.

Potato the most allergenic

Potato is by far the commonest nightshade to cause illness, perhaps because it is such a common daily food. Sometimes the discovery resulted unintentionally from a shortage of potatoes, or the clue was a reaction to tobacco smoke in a pub, now very rare. It is curious that no obvious effects of actually smoking tobacco were reported. There is good evidence that the effects on the nervous system and behaviour may be caused by the alkaloids in the nightshades which can interfere with neurotransmitters in the brain, and of course tobacco is very addictive.

Dr Norman Childers, an eminent botanist at Rutgers University, discovered that his disabling rheumatism vanished when he avoided the nightshades. He researched this closely, wrote books and scientific papers about this avoidable cause of rheumatism, and set up the "Arthritis Nightshade Research Foundation" which is still active and easily found on the internet. I have seen many cases where arthritis was due to food, most often milk, but very rarely to the nightshades.

Drugs only suppress

Everyone wants the magic pill to banish their all their ills, but in chronic problems such as asthma or arthritis drugs only suppress symptoms, may cause side-effects, and never cure. The concept of trying to find a cause and avoid it is very seldom considered today yet there is no reason why restricted diets could not be introduced at the same time as the suppressive drugs. If the cause is a food or foods the drugs might be withdrawn without relapse of the chronic problem being treated. Today suppression is the rule, at vast cost to the NHS, and side-effects are common. I have seen patients who complained that their doctor was looking at the computer during the consultation instead of looking at the them, and never seeing the same doctor twice.

Anyone who suspects that their problem might be related to food intolerance should keep detailed food diary, recording everything that passes the lips. In time the diary may show a relationship between symptoms and eating a specific food. The next step could be a test diet for up to three weeks living on nothing else but the few foods which very seldom cause trouble. This approach applies to any food intolerance as well as potato, and nutritional deficiencies do not occur in only three weeks. If the complaints do not improve you have shown that food allergy or intolerance is very unlikely, so go back on a normal diet and forget it. Never continue dieting any longer than three weeks. (I have given much more detailed suggestions for self diagnosing food intolerance here.)

If the problem, whatever it may be, gets better this suggests that food is the cause. The restricted few foods diet should continue while test feeds are given to confirm which food, or foods, reproduce the symptoms. One reaction to a food could be coincidence, so do not jump to conclusions. It is never possible to be sure that a specific food is the causing trouble unless a test feed causes a reaction every time it is eaten.

Nota Bene

These comments apply only to food intolerance, where the food triggers a delayed reaction the following day and normal amounts of the suspect food are required to cause a reaction. Any suggestion that you react quickly to a small amount of any suspect food means that you may be dangerously allergic and should never risk a test feed. I cannot be responsible for the effects of dieting, and you must discuss with your doctor before deciding to experiment with diets.

For more detailed information about potato intolerance and a wide range of other allergies and intolerances consult Dr Morrow Brown's excellent website at www.allergiesexplained.com

For letters to Dr Morrow Brown from two families who had had severe problems with potato/nightshade allergy click here.